Vacuum friction pad for tape recorders



Aug. 1, 1961 D. G. c. HARE VACUUM FRICTION PAD FOR TAPE RECORDERS FiledOct. 24, 1958 N 4 mm WW Wm T M x )Wf WW Patented Aug. 1, 1961 2,994,489VACUUM FRICTION PAD FOR TAPE RECORDERS Donald G. C. Hare, New Canaan,Conn., assignor, by mesne assignments, to Sangamo Electric Company,Springfield, 111., a corporation of Delaware Filed Oct. 24, 1958, Ser.No. 769,402 '7 Claims. (Cl. 242-5751) The present invention relates toimprovements in vacuum friction pads for tape recorders.

In the design of modern magnetic tape record-reproduce machines,particularly those designed for the storage of analog and digital data,the problem of adequate control of the tape, both as to tension andposition, has become increasingly important. The earlier methods ofusing the tension produced by the reed motors themselves are no longeradequate, particularly when it is important to divorce any possible tapedisturbance due to the reels from the section of tape just before andafter it passes over the record-reproduce head. Further, the use ofslack loop systems, in which the tape is more or less uncontrolled insome part of its path, requires that a friction or similar tensioningdevice be used in the vicinity of the head itself. Finally, in the caseof high speed start-stop systems, where it is vital that the flow of thetape be started and stopped in a few milliseconds without any creep, hasled to the design, in some cases, of rather elaborate tensioningsystems. Among the tensioning systems in use for this type of machineare such things as a felt pad which will hold the tape against a metalblock or another similar pad, idlers whose high friction surfaces whichdrive a shaft which is affected by either viscous or coulomb friction,as well as a rather large variety of vacuum tensioning pads.

These vacuum friction pads comprise tape guiding surfaces having suctionapertures therein through which the vacuum or suction acts to hold thetape pressed against the guiding surface.

Much difficulty has heretofore been encountered with prior vacuumfriction pads because of the tendency of these pads to clog by reason ofparticles of the oxide coating on the magnetic tape, together with otherforeign particles on the tape, tending to build up accumulations on thevacuum pad, with the resulting failure of the pad to act properly on thetape, or to damage the tape. This build-up of oxide coating starts as asmall point deposit, and then proceeds to build up by accretions ofoxide coating, together with other foreign particles, to this pointdeposit. Such build-up of coating from the tape commonly causes improperguidance and inadequate tension on the tape, together with damage to thetape; and necessit-ates frequent stopping .of the machine for cleaningor substituting vacuum pads.

As a result of extensive experimentation and development, I have devisedan improved vacuum friction pad which avoids or greatly reduces theabove difiiculties. The construction and proportions of this improvedvacuum pad will now be explained in connection with the followingpreferred embodiment of the invention, as illustrated in theaccompanying drawing in which:

FIGURE 1 is a plan view of the improved vacuum friction pad, on agreatly enlarged scale;

FIGURE 2 is a longitudinal sectional view taken approximately on theplane of the line 2-2 of FIGURE 1;

FIGURE 3 is a transverse sectional View taken approximately on the planeof the line 33 of FIGURE 1;

FIGURE 4 is a fragmentary sectional view, similar to FIGURE 2, but on aconsiderably magnified scale .to illustrate the up and down undulationsof the tape in its travel as it passes over the slots and lands of myimproved vacuum pad; and

FIGURE 5 is a fragmentary transverse sectional view, similar to FIGURE3, but illustrating a modified embodiment.

In these figures, my improved vacuum friction pad is designated 10 inits entirety, and the magnetic tape which is guided and tensionedthereby is designated T, these parts being shown on a considerablyenlarged scale. These vacuum pads are usually mounted in proximity to arecording, reproducing or erasing head, one of which is fragmentan'lyindicated at H in FIGURE 1. The vacuum pad is usually secured in amounting block 12 which is readily removable and replaceable in therecording and reproducing machine, in order to facilitate ready mountingand removal of the vacuum pad. The mounting block 12 is shown as havingan upwardly projecting portion 14 which is provided with achannel-shaped mounting slot 16 extending longitudinally therethrough.The vacuum friction pad 10 is releasably held in this channel-shapedmounting slot 16 by set screws 18 (preferably of the Allen head type),which screw through threaded holes in one side wall of the mounting slot16.

The pad 10 comprises a long rectangular block of metal 20, in which iscored or drilled a longitudinally extending vacuum duct 22. One end ofthis duct is closed, but secured to the other end, as by soldering,brazing or threading is a vacuum tube 24, preferably metallic, whichextends to a source of suction in the machine. The degree of suction orvacuum may be varied, depending upon the thickness of the tape, thedegree of tension desired, etc., being generally of the order ofapproximately 3 to 12 inches of mercury.

interposed between the side walls of the channel-shaped mounting slot 16and the adjacent side walls of the pad block 20 are thin vertical plates26 which have their top edges projecting slightly above the top edges ofthe pad block 20 so as to define a tape guiding channel 30 extendinglongitudinally of the pad block. These plates 26 also function as shimplates for accommodating different thicknesses of pad block within thechannel-shaped mounting slot 16.

Formed in the longitudinal tape guiding surface 31 of the pad block 20are a series of transversely extending suction slots 32, which arespaced apart by transversely extending intervening lands 34. The suctionslots 32 extend down into the pad block 20 sufiiciently to intersect thesuction duct 22, from which they all derive suction transmitted throughtube 24. As shown in magnified scale in FIGURE 4, the upper oppositecorners or edges of each transverse land 34 are rounded or curved, asindicated at 34, so as to enable the tape T to depress or cup downwardlymore readily into each suction slot 32, as will be later described ingreater detail.

In the preferred embodiment of the invention the suction slots 32 do notextend out to the full width of the tape T, or to the full width of thetape guiding channel 30. Instead, the opposite ends of these suctionslots terminate slightly short of the side walls of the tape guidingchannel 30, so as to leave narrow longitudinally extending lands 36along which the side edges of the tape T can bear in the travel of thetape through the guide channel 313. These longitudinally extending lands36 may be formed integral with the pad block 20; or as an alternativeconstruction, illustrated in FIGURE 5, the slotted portion of the padblock 20 may be made slightly narrower than the width of the guidechannel 30, with the ends of the suction slots 32 extending out to thesides of the pad block, and with the longitudinal lands 36 in the formof strips 36 secured over the open ends of the suction slots, and withtheir top edges lying flush with the top edges of the transverse lands34.

As a result of extensive research and experimentation, I have found thatthe build-up of oxide coating on the vacuum pad 10 can be entirelyprevented, or reduced by a very large percentage over priorconstructions, when the suction slots 32, transverse lands 34 andlongitudinal lands 36. bear a certain approximate dimensionalrelationship to the tape T and to each other. For example, for thestandard magnetic tape. having a conventional width of approximately /4inch and a conventional thickness ranging from /2 to 1 /2 mil (mylar oracetate backing), I have found that optimum results are obtained whenthe transverse lands 34 have a width or thickness substantially as smallas A of an inch (0.015 inch), and the suction slots 32 havesubstantially the same width. The narrowness of such transverse lands 84does not afford adequate surface area for the build-up of oxide coatingto start, or to progress to the point where an objectionableaccumulation can occur. For example, the narrowness of the lands 34results in accumulations of oxide coating breaking off at the trailingedges of these lands, before they can assume any objectionable size, andbeing then instantly sucked into the suction slots 32. The abovepreferred or optimum thickness of the transverse lands (approximately.015 inch) avoids the previous tendency of accumulating objectionableaccretions of oxide coating from the tape T, without producingobjectionable wear on the tape. That is to say, if, on the other hand,these transverse lands 34 are made excessively thin, they result inupper knife-like edges which produce undue wear on the tape.

With regard to the suction slots 32, optimum results appear to beattained when the slots have substantially the same ratio of width asthe lands 34, i.e. approximately .015 or ,4 of an inch. This widthallows the tape T to depress or cup down slightly under the action ofsuction in its travel over each suction slot, as shown in greatlymagnified scale in FIGURE 4. Thus, the tape goes through a series ofvery slight up and down undulations in traveling across the series oflands and slots, which is desirable for augmenting the tension on thetape. Making the slots too wide makes the undulations too pronounced forhigh running speeds of the tape, and making the slots too narrowdiminishes the tension on the tape objectionably. In keeping with thisundulating travel of the tape, the corners or edges of each land 34 arerounded or curved at 34 to minimize wear on the tape, both corners oredges being rounded where the tape is intended to be under vacuumtension in each direction of travel. The radius of curvature of eachrounded edge 34' is preferably so proportioned to the extremely thinWidth of each land 34 that the convex curvatures at the opposite edgesof each land intersect at the top'of the land, as shown inFIGURE 4,whereby no flat surface remains on the top of each transverse land 34,but instead each of these lands presents to the under face of the tape Ta completely curved convex surface having no shoulders or angular edges.The absence of such shoulders or angular edges aids in minimizing thebuild-up of oxide particles, which do not start to adhere as readily toacurved surface as they do to a right angle shoulder or angular edge.

Referring now to the lands 36 extending longitudinally along the sidesof the guide channel 30, I find that optimum results are obtained ifthese lands have a width of the order of 0.010 inch. If theselongitudinal lands 36 are substantially narrower than this there is sometendency to deform and draw in the edges of the tape; and there is alsoa tendency for considerable oxide to build up in the longitudinalcorners between the side walls 26 and the pad block 20. If thelongitudinal lands are made considerably wider than this optimumdimension there is an objectionable loss of effective tape width for thesuction to act on in producing the desired tape tension.

Any tendency to accumulate oxide coating at the leading and trailing endsurfaces of the pad block 20 is prevented by depressing or recessingthese surfaces below 4 the top level of the slots 32 and lands 34, asindicated at 38, 38' in FIGURE 2.

I have obtained very satisfactory performance over long periods of timewhen using vacuum friction pads of substantially the foregoingdimensions, wherein the active area of each pad was approximately 1 inchlong and inch wide, with approximately thirty-two suction slots 32 tothis 1 inch of lengthwhen using magnetic tape of A inch width and /2 to1 /2 mil thickness. It will be understood that these dimensions may besubject to appreciable change when using other widths of tapes, andpossibly other thicknesses of tapes.

I claim:

1. A vacuum friction pad for tensioning and guiding a run of magnetictape, comprising a mounting block having a mounting channel therein, apad block in said channel, a vacuum chamber in said pad block, a tapeguide surface defining one side of said pad block, said tape guidesurface comprisisng a plurality of alternating slots and lands extendingtransversely of the direction of travel of the tape across said pad,said slots transmitting suction from said vacuum chamber to theunderside of the tape, said lands being relatively narrow, of a width ofapproximately 0.015 inch to prevent objectionable accumulations of oxidecoating from the tape upon the pad, said lands also having rounded upperedges to facilitate the downward depression of the tape into each slotunder the action of suction, whereby the tape makes a series of up anddown undulations as it passes across the slots and lands, and guideplates interposed between the sides of said mounting channel and thesides of said pad block for defining the side edges of the tape guidingchannel.

2. A vacuum friction pad for tensioning and guiding a run of magnetictape, comprising a mounting block having a mounting channel therein, apad block in said channel, a vacuum chamber in said pad block, a tapeguide surface defining one side of said pad block, said tape guidesurface comprising a plurality of alternating slots and lands extendingtransversely of the direction of travel of the tape across said pad,said slots transmitting suction from said vacuum chamber to theunderside of the tape, said slots and lands both being relatively narrowand of substantially the same width of approximately 0.015 inch toprevent objectionable accumulations of oxide coating from the tape uponthe pad, said transverse slots extending out to the sides of the padblock, and longitudinally extending lands in the form of strips securedover the open ends of said transverse slots and having their top edgeslying flush with the top edges of said transversely extending lands.

3. A vacuum friction pad for tensioning and guiding a run of magnetictape, comprising a vacuum chamber, a tape guide surface defining oneside thereof, said tape guide surface comprising a plurality ofalternating suction slots and lands extending transversely of thedirection of travel of the tape across said pad, said slots transmittingsuction from said vacuum chamber to the underside of the tape, and saidlands being relatively narrow, of a width of approximately 0.015 inch toprevent objectionable accumulations of oxide coating from the tape uponthe pad.

4. A vacuum friction pad for tensioning and guiding a run of magnetictape, comprising a vacuum chamber, a tape guide surface defining oneside thereof, said tape guide surface comprising a plurality ofalternating suction slots and lands extending transversely of thedirection of travel of the tape across said pad, said slots transmittingsuction from said vacuum chamber to the underside of the tape, and saidslots and lands being substantially the same width, of approximately0.015 inch to prevent objectionable accumulations of oxide coating fromthe tape upon the pad.

5. A vacuum friction pad for tensioning and guiding a run of magnetictape, comprising a vacuum chamber,

a tape guiding channel in one side thereof, said tape guiding channelcomprising a plurality of alternating suction slots and lands extendingtransversely of the direction of travel of the tape through saidchannel, said suction slots transmitting suction from said vacuumchamber to the underside of the tape, said suction slots andtransversely extending lands both being relatively narrow, saidtransversely extending lands being of a width of approximately 0.015inch to prevent objectionable accumulations of oxide coating from thetape upon the pad, and longitudinally extending lands between the endsof said suction slots and the sides of said tape guiding channel, saidlongitudinally extending lands also being relatively narrow.

6. A vacuum friction pad for tensioning and guiding a run of magnetictape, comprising a vacuum chamber, a tape guiding channel in one sidethereof, said tape guiding channel comprising a plurality of alternatingsuction slots and lands extending transversely of the direction oftravel of the tape through said channel, said suction slots transmittingsuction from said vacuum chamber to the underside of the tape, saidsuction slots and transversely extending lands both being relativelynarrow, and longitudinally extending lands between the ends of saidsuction slots and the sides of said tape guiding channel, saidlongitudinally extending lands being of a narrow width of theapproximate order of 0.010 inch, and said transversely extending landsalso being of a narrow width of approximately 0.015 of an inch andhaving convexly rounded upper edges over which the magnetic tapetravels, whereby to prevent objectionable accumulations of oxide coatingfrom the tape upon the pad.

7. A vacuum friction pad for tensioning and guiding a run of magnetictape, comprising a mounting block having a mounting channel therein, apad block in said channel, a vacuum chamber in said pad block, a tapeguide surface defining the outer side of said pad block, said tape guidesurface comprising a plurality of alternating slots and lands extendingtransversely of the direction of travel of the tape across said pad,said slots transmitting suction from said vacuum chamber to theunderside of the tape, said transversely extending slots extending outto the side surfaces of the pad block, and removable shim platesinterposed between the sides of said mounting channel and the sides ofsaid pad block, said transversely extending slots and lands both beingrelatively narrow, and of substantially the same width of approximately0.015 inch to prevent objectionable accumulations of oxide coating fromthe tape upon the pad.

References Cited in the file of this patent UNITED STATES PATENTS2,393,243 Franz Jan. 22, 1946 2,615,656 Strake Oct. 28, 1952 2,746,749Huck May 22, 1956 2,778,634 Gams et a1. Jan. 22, 1957

